Coupling devices, such as clutch plates for detachably mounting various maintenance elements (i.e., brush, pad holder) to floor maintenance machines are known. Many floor maintenance machines include a motor driven drive shaft and hub that is provided with radially extending lugs located near a terminal end. An annular clutch plate is secured to the maintenance element and includes structure engageable by the lugs on the drive hub. In particular, the clutch plate includes a central opening having radial recesses that enable the lugs to pass through the clutch plate when the drive hub is inserted into the clutch plate. After insertion, the clutch plate is rotated relative to the drive hub which causes the lugs to move axially behind the clutch plate to secure the maintenance element to the shaft. In at least one type of prior clutch plate, solid cast ramps (aluminum) were provided so that the lugs ride up the ramps until the lugs jam against the ends of ramps in the installed position to effect securement.
It has been recognized that such prior coupling arrangements are not completely satisfactory. For example, in these maintenance machines, the high-starting torque often times causes the clutch plate to become tightly wedged in place since the coupling is designed such that operating rotation of the machine drive hub tends to tighten the coupling. In other words, the coupling is designed to lock in the direction of operating rotation of the machine drive hub. Accordingly, with this wedging or binding affect, it becomes difficult to remove the maintenance element for any purpose. In addition, such wedging or binding, whether caused by the high-starting torques or by reason of the assembly or construction of the coupling itself, causes not only undue wear, but possible damage to the drive lugs and/or clutch plate that not only creates costly replacement problems, but also results in extended operator and machine downtime.
Furthermore, this wedging or binding action often times causes abrading of the lugs or ramps so that it is difficult to achieve a tight coupling between the component parts with the ultimate result that the maintenance element acts to oscillate off center or vibrate to the extent that good results cannot be achieved in the floor to be cleaned, polished, scrubbed or the like. In other words, such a condition results in an unsatisfactory floor finish. Still further, such prior coupling arrangements require the operator to lift or tilt the machine in order to enable the operator to manually engage the clutch plate member to the lugged shaft. This, of course, requires additional operator time that often times prompts the operator not to take the time to replace the maintenance element after it has become soiled or damaged, resulting in unsatisfactory performance. Further, such failure to remove the maintenance element can result in actual destruction to the element due to the machine weight, particularly after prolonged periods of time in storage.
A further problem with prior coupling devices relates to the "galvanic" action between the dissimilar metals (i.e., aluminum to steel) on the drive hub and the clutch plate. This combination results in corrosion between the parts and compounds the "galling" of the lugs or ramps that makes it extremely difficult to remove the brush or pad holder from the machine. This problem can become extremely severe in moist and/or wet conditions and where chemicals are introduced that act to accelerate the corrosion between the parts. Accordingly, when the clutch plate has to be broken away from the lugs, the opportunities to reuse the clutch plate without repair are minimized since the plate does not effectively accommodate (i.e., size and shape) itself to the drive lugs.
An improved coupling device for floor maintenance machines is described in U.S. Pat. No. 4,391,548, which alleviates at least some of the problems described above. The coupling device for floor maintenance machines described in this prior patent is arranged and constructed to enable automatic coupling and de-coupling of the maintenance element (i.e., brush, buffing pad holder or the like) without direct manual implementation thereof. This coupling device improves on the prior art and has performed satisfactorily.
It has been found, however, that the diameter of the maintenance machine drive hub can vary slightly from machine to machine. Because of this potential variance in diameter, the coupling between the machine drive hub and the pad holder assembly may not be centered. Additionally, the length of the drive hub can vary from machine to machine and accordingly, there can be axial "slop" between the coupling device and the lugs of the drive hub when the coupling device is mounted on the hub.
It is important that the buffing pad or cleaning brush be able to be quickly and easily installed and removed from the maintenance machine. The coupling device must securely mount the buffing disk or brush on the shaft consistently regardless of slight variance in drive hub dimensions from machine to machine.